The children on board the Sewol were told to stay put in their cabins, where they waited for further orders. The confirmed death toll on Sunday was 187.

As part of the investigation, prosecutors raided two shipping safety watchdogs and a coastguard office. They have also raided two vessel service centers, which act as maritime traffic control.

Chung's offer to resign has to be approved by President Park Geun-hye, who has the most power in government.

"Keeping my post too great a burden on the administration," a somber Chung said in a brief announcement. "... On behalf of the government, I apologize for many problems from the prevention of the accident to the early handling of the disaster."

Chung was booed and someone threw a water bottle at him when he visited grieving parents the day after the disaster. President Park was also booed by some relatives when she visited a gym where families of the missing were staying.